Sign detecting system



SIGN DETECTING SYSTEM 5 Sheets-Sheet l Filed Aug.

y 28, 1968 SH INTARO OSHIMA ETAL 3,385,976

SIGN DETECTING SYSTEM Filed Aug. 25. 1964 I 3 Sheets-Sheet 2 e "mum mnum unmm mum United States Patent 0" 3,385,976 SIGN DETECTING SYSTEM Shintaro Oshima, Musashino-shi, Hajime Enomoto, Sugano-machi, Shiyoji Watanabe, Tokyo-to, and Yasuo Koseki, Chofu-shi, Japan, assignors to Kokusai Denshin Denwa Kahushilti Kaisha, Tokyoto, Japan, a joint-stock company of Japan Continuation-in-part of application Ser. No. 50,689, Aug. 19, 1960. This application Aug. 25, 1964, Ser. No. 391,885

4 Claims. (Cl. 387-88) This is a continuation-in-part of our application Ser. No. 50,689, filed Aug. 19, 1960, now Patent No. 3,191,053.

The present invention relates to a sign detecting system, more particularly to a system for detecting the plus or minus polarity of the difference between a direct-current input signal and a direct-current reference signal by the use of non-linear elements having substantially a symmetrical hysteresis characteristic with respect to its original point as term-magnetic cores or ferro-electric material.

In the above-mentioned system, it is necessary for precisely detecting the polarity of an electric signal that a detecting means including the non-linear elements is unaffected by the preceding polarization of the non-linear elements even if the hysteresis of said polarization has passed along any course. This fact is most important for the sign detecting circuit. Hence, it is necessary for constructing a precise analogue-digital converter to select only non-linear elements each having an original point which has no relation to the prior hysteresis of the polarization. The original point will be denoted hereinafter as zero point.

The drift ofthe zero point makes it difficult to obtain an analogue-digital converter having great accuracy.

The present invention further relates to a system for converting the sign of a direct-current signal to an alternating-current high frequency signal having a 0 phase or r phase. It has been well-known, in one of such systems as described above, to employ a magnetic amplifier obtaining a double frequency of the energizing current thereof. In this magnetic amplifier, however, when a relatively large direct-current passes through the amplifier, a residual magnetism will be created in the core or cores of the magnetic amplifier by the direct-current due to the hysteresis characteristic of the magnetic core, and the residual magnetism will remain in the magnetic core or cores for a long time. This defective characteristic appears always in a device using a ferro-rnagnetic material or a ferro-electric material. Hence, it is generally difiicult to construct a very precise sign detecting device having a very stable zero point.

An essential object of the present invention is to obtain a very precise sign detecting circuit having a very r stable zero point.

The novel features which are believed to be characteristic of the present invention are set forth with particularity in the appended claims, but the present invention, both as to its construction and manner of operation, together with further objects and advantages thereof, may be understood =by references to the following description taken in conjunction with the accompanying drawings, in which the same members are indicated by the same numerals, and in which:

FIG. 1 is a connection diagram for describing the principle of the present invention;

FIG. 2 is a characteristic curve and wave diagram for describing the operation of the circuit shown in FIG. 1;

FIG. 3 is a connection diagram of one example of the present invention;

FIG. 4 is a wave diagram for showing an example of 3,385,976 Patented May 23, 1968 ice control time chart for describing the operation principle of the system of the present invention;

FIGS. 5 (A) and (B) are characteristic curves for describing an operation principle of the system of the present invention;

FIGS. 6(,A) and (B) are embodiments of windings wound on magnetic cores to be used in the embodiment of the present invention;

FIG. 7 is a connection diagram for showing the other example of the present invention;

FIG. 8 is a connection diagram for showing another example of the present invention;

FIG. 9 is a characteristic curve for describing the operation of the example shown in FIG. 8;

FIG. 10 is a characteristic curve for describing operation of another example of the present invention;

FIG. 11 is a connection diagram for showing an application of the system of the present invention;

FIG. 12 is a connection diagram of another example of the present invention; and

FIG. 13 is a connection diagram for another example of the present invention.

The principle of the present invention will be first described in connection with FIG. 1. The circuit of FIG. 1 consists of two ferro-magnetic cores M and M three windings N N and N an input impedance Z connected to the winding N and an output impedance Z connected to the winding N Each of the windings N N and N is composed of a coil wound on the magnetic core M and another coil wound on the magnetic core M As shown in FIG. 1, the windings N N and N are wound in such a manner that all coils of the windings N and N 3 are wound on the magnetic cores M and M in the same polarity, and one coil of the winding N is wound on the same polarity as that of the coils of the windings N and N on the core M and the other of the winding N is wound in the reverse polarity as the windings N and N on the core M The operation principle for getting an even harmonic frequency of the exciting current is as follows. In the circuit of FIG. 1, let it be assumed that the magnetization characteristics of the cores M and M are such as shown in FIG. 2, (a).

Then, when an input signal current 1 is impressed on the winding N and a high frequency exciting current if is applied to the winding N and the amplitude of the current i is sufficiently large enough to make operation along the major hysteresis loop of the cores M and M possible is shown in FIG. 2, (b), Where the solid line is the wave form of the exciting current i for the core M and the broken line is the wave form of the exciting current i for the core M Then, the output voltages are induced across both of the output coils wound on the cores M and M respectively, thus inducing an output voltage across the terminals of the winding N The states of the output voltages across the terminals of the winding N varies according to the polarity of the input signal current 1 In this case, there are three states.

(i) If I =0, then, the induced voltages across respectively the output coils of the cores M and M are always of an equal amplitude and opposite phase, so that no voltage is induced across the terminals of the winding N as shown in FIG. 2, (e).

(ii) If l 0', then the induced even harmonic voltage V induced across the output coil of the core M becomes larger than that of the core M and both of the induced voltages are in phase, so that the even harmonic frequency voltages e of the exciting current are induced across the terminals of the winding N as shown in FIG. 2, (1). And in this case, the even harmonic components in the output signal have a 0 phase as shown in FIG. 2, (f).

(iii) On the contrary, if I O, then the induced even harmonic voltage V induced across the output coil of the core M becomes larger than that of the core M and both of the induced voltages are in phase so that the even harmonic voltages e of the exciting current are induced across the winding N and the even harmonic components of the output voltage have a 1r phase, as shown in FIG. (a)- From the above descriptions, the phase of the even harmonic components in the output voltage induced across the winding N is completely dependent on the sign of the input signal.

Then, if we detect the phase of the even harmonic components of the output voltage across the winding N we can detect the sign of the input signal.

When it is assumed that the magnetic cores M and M have such BH characteristics having no hysteresis as shown in FIG. 2, there is no drift of the zero point of the magnetic core. Generally, however, a magnetic substance has a hysteresis characteristic. This hysteresis effect, as shown in FIG. 2, is equivalent to the case wherein a zero point displaced by AH from the prior zero point is taken as the new zero point. The magnetic field intensity AH is due to the effect of the preceding signal. However, if two magneto cores M and M are combined in such a manner that the displacements AH and AH of the mag netic field intensities in the magnetic cores M and M due to their preceding hystereses take the following relations just before the sign detection, then AH1=AHZZO OI AHI:AH2

the resultant displacement AH becomes equal to whereby drift of the zero point can be completely eliminated.

The present invention relates to a new sign detecting system in which the resultant residual magnetism is always made zero just before the sign detection so as to eliminate the above mentioned drift of the zero point by using a setting signal.

Among two conditions (AH =AH =0 or AH =AH for eliminating the resultant residual magnetism, the condition (AH =AH =0) can be obtained by impressing, on the cores, a gradually damped alternating magnetic force as a setting signal, having an amplitude which is sufficiently larger than the coercive-force of the magnetic cores, just before the sign detection so as to eliminate completely the resultant residual magnetism. Demagnetization is performed through this process. The condition (AH =AH =0) can also be obtained by making the component in the direction of the magnetic field due to input signal current applied to the input winding zero by using a setting signal which is employed to direct the polarity of the residual magnetism towards the direction perpendicular to the magnetic field generated by the input signal current and the output current winding wound on the magnetic cores.

For obtaining the condition (H =H =H in the circuit of FIG. 1, it is only necessary to supply both a certain direct current of a constant value and an alternating current to the exciting winding N or to impress transiently a sufficiently large direct current; or alternating current; in such a manner that both of the absolute values of the residual magnetisms of the magnetic cores become the value H In FIG. 3, in input signal winding N an exciting winding N and an output winding N are wound on two ferrite cores M and M having substantially symmetrical hystereis characteristics with respect to their original zero points.

The effect of the setting signal in this invention will be explained in connection with FIG. 3, as follows. As we have described above, the setting signal is indispensaable for attaining a highly precise detection of a sign, and the setting signal may be an alternating current signal, a direct current signal or a superimposed signal of said alternating-current signal and said direct current signal, but for simple explanation we consider only the case where an alternating-current signal is used as a setting signal hereafter.

As shown in FIG. 3, the windings N N and N are wound in such a manner that all coils of the windings N and N, are wound on the magnetic cores M and M in the same polarity, and one coil of the winding N is wound in the same polarity as that of the coils of the windings N and N on the core M and the other coil of the winding N is wound in the reverse polarity as the windings N and N on the core M An input signal current I is applied to the winding N through an input resistor R and a demagnetizing signal current i having a high frequency and an exciting signal current i having a high frequency f are successively applied to the winding N A resistor R is a coupling resistor, and a capacitor C and an inductor L construct a parallel tuned circuit for a frequency 2 The output signal having the frequency 2f is led out through the secondary windings of the tuned circuit,

We consider the case where the currents shown in FIG. 4 are applied to the circuit of FIG. 3.

A demagnetization current i (referred to as a setting signal in this invention) is a gradually damped high frequency exciting signal, and its peak amplitude is large enough to cover the coercive force of the magnetic core.

According to said setting operation by the current i the residual effects of the preceding signals (AH and AH for cores M and M becomes, respectively zero, and both of the cores M and M are reset to zero point.

Next, the sampled input signal I and the exciting current of high frequency 1 are simultaneously applied to the windings N and N respectively.

Then as explained with reference to FIG. 2, even harmonic voltages are induced across the winding N In this case only the double frequency component is selectively tuned with the circuit LC and the double frequency voltage whose phase corresponds to the polarity of the input signal is obtained at the output terminals through the coupling resistor R The demagnetization is performed by using the setting signal as described above, that is, the deviation AH becomes zero, and when an exciting signal current i; and the input signal I are applied simultaneously to the abovementioned elements of FIG. 3, the input signal is converted to an even harmonic voltage without any drift of the zero point.

Let it be assumed that the magnetic characteristics of the magnetic cores M and M are such as shown in FIG. 5 (A). Then, when the input signal of direct current I is supplied to the winding N and the high frequency setting current i is supplied to the winding N the amplitude of the current i being sufficiently large so as to produce a sufficiently larger magnetic field than the coercive force H and the attenuation locus of said amplitude describing a gentle envelope such as shown in FIG. 503), a residual magnetism gb will remain in the magnetic core M when the current i becomes zero and the current I, also becomes zero.

On the other hand, since the current i is the reverse phase against the former case relative to the magnetic core M an inverse excitation is given to the core M as shown in FIG. 5 (B) by broken lines. However, the polarities of the residual magnetism of the magnetic cores M and M are the same to each other, because the current I is supplied to the cores in the same polarity.

Then, we consider the case where the continuous input signal current I is applied to the input signal winding.

The frequency of the input signal 1 is much lower than that of the setting signal frequency and the exciting signal frequency, and is also lower than the repetition cycle of the exciting signal.

After application of the setting signal, both of the cores M and M are magnetized to a certain magnitude of residual magnetism corresponding to the magnitude of the input signal at the setting period, so that when an exciting signal is applied to the elements, the input signal at the exciting period and the residual magnetism effect induce even harmonic output voltages; then a high accuracy in analogue-digital conversion is attained.

In the case where the sampled input signal is applied to the elements, there is no input signal at the setting period and the setting effect results in no resultant of the preceding input signal and sign detection will be attained at the next sampling period without any drift of the zero point. On the contrary, in the case where the continuous input signal is applied to the elements, a certain magnitude of residual magnetism corresponding to the input signal of the setting period remains. That is, the cores M and M memorize the magnitude of the print signal in the state of residual magnetism and at the next sampling period the input signal to be added with the said residual flux magnetism determines the phase of the even harmonic output voltage more quickly and more precisely in comparison with the case of sampled input signal.

As explained before, there is another method to obtain the condition (AH =AH for the elimination of the residual magnetism of the preceding input signal.

As shown in FIG. 6, the direction of the setting magnetization is perpendicular to the direction of magnetization generated by the input signal current and the excitation signal.

Accordingly, when a direct current pulse signal, whose amplitude is large enough to cover the coercive force in the setting field direction, is applied at the setting time the residual magnetism of the preceding input signal is effectively eliminated, and there is no drift of the Zero point for the next sign detecting period.

For simplification 0f the explanation, We describe the case in which, as shown in FIG. 3, a selective resonant circuit LC tuned to a freqency 2 which is twice the exciting frequency f is connected in cascade to the output winding N through a coupling resistance R and an output voltage having frequency 2 is led out of the output terminal 0 In this case also, as described above, the polarity of the output voltage e becomes 0 phase or 1r.-phase in accordance with the positive or negative polarity of the input current I and moreover, when the frequency of the exciting current i is selected so as to be sufficiently large in comparison with that of the input signal current I and the number of turns of the windings N and N are suitably selected, a large voltage gain due to the difference between the frequencies of the currents i and 1 will be obtained. Accordingly, it is possible to detect the sign of the small signal input current I by amplifying and demodulating the output voltage e According to the present invention, by supplying a setting signal i to the exciting winding before supply of the exciting current i and the signal input current I we establish the intrinsic symmetry of the magnetic element to make the magnetic hysteresis characteristic of said element irrelevant to the magnitude of the residual magnetism, and by detecting the phase displacement of the output voltage e By such a method as described above, it is possible to discriminate the polarity of very small input current in a highly precise manner.

The above description relates to the case in which ferromagnetic elements are used, but the same principle as the above-mentioned magnetic elements can be'easily applied to the case in which ferroelectric elements are used in the place of ferromagnetic elements, by exchanging an electric voltage for the electric current. An example of such a case is shown in FIG. 7, in which the circuit consists of two ferroelectric elements C and C having the same symmetrical nonlinear characterstic, two coupling condensers C and C having the same capacity, two damping resistors R and R having the same resistance, an output transformer T of balance type, input terminals 1 and 2, and output termials 5 and 6, said members being connected as shown in FIG. 7.

In the circuit of FIG. 7 also, such elimination of the residual polarization and establishment of the symmetrical condition of the zero point as in the case in which ferro-magnetic elements are used, can be attained by impressing a depolarizing electric voltage on the terminals 3 and 4, and then by impressing an input voltage and a high frequency exciting voltage, respectively, on the terminals 1, 2, and 3, 4. In this case, an even order higher harmonic voltage of the exciting signal is generated in a closed loop circuit consisting of the members C C R TR -C C The phase of the generated higher harmonic voltages becomes 0 or 1r phase in accordance with the polarity of the input signal, these voltages are led out of the output terminals 5 and 6. In the closed loop circuit, when capacities of the capacitors C and C and inductance of the primary winding of the transformer T are so selected that the circuit resonates with the second hormonic of the exciting wave, a voltage e; having frequency 2 appears at the output terminals 5 and 6.

The description of FIG. 3 relates to the case in which only the input current I and the exciting current i having frequency f are supplied, respectively, to the windings N and N However, besides the currents one high frequency current i having frequency f may be applied to the winding N In this case, a modulation product of frequencies (f+f and (ff will be obtained out of the output terminals of the winding N When one of the modulation components is selectively taken out, it is possible to obtain an electric output voltage having one or" two possible phase positions which differ by to each other in accordance with the polarity of the input current I We have described a circuit capable of detecting the polarity of a small or weak signal by utilizing ferro-magnetic or ferroelectric elements having a symmetrical hysteresis characteristic. However, in the circuit, it is possible to obtain an even order higher harmonic oscillation by feeding back a particular even order higher harmonic component to the input signal I by means of an internal feedback or an external feedback of the higher harmonic. In this case also, the oscillation phase is controlled by the polarity of the input signal I whereby the polarity of the input signal I can be discriminated. In the following will be described the case of a second harmonic oscillation. FIG. 8 shows a connection diagram for illustrating the principle of a circuit which can detect the polarity of the input current according to the oscillation such as described above.

The circuit of FIG. 8 consists of a pair of ferro-magnetic cores M and M an input winding N an exciting and setting winding N an output winding N a capacitor C, and a coupling resistor R The windings are wound on the cores in such a manner that the windings N and N; are of the same polarity relative to the cores M and M the winding N has the same polarity as the windings N and N on the core M and the reverse polarity to the core M and all the coils of all windings are connected in series.

Let it be assumed that a relatively large exciting current i is supplied to the winding N When input current I having a suitable amplitude is supplied to the winding N an even order higher harmonic voltage of the exciting current i will develop in the winding N The phase of the second harmonic voltage is determined by the polarity of the input signal current I And if the second harmonic voltage is generated, a second harmonic oscillation will be built up in the output circuit consisting of the winding N and the capacitor C. This generation is caused by a so-called parametrical oscillation. The oscillation phase is subjected to the induced voltage. If the input current I varies a positive value from a negative value, the oscillation phase of the output second harmonic voltage e reverses abruptly as shown in FIG. 9. This fact has been proved by the inventors experiments.

In FIG. 9, the input current 1 and the second high harmonic output voltage e are, respectively, taken on the abscissa and ordinate. In this characteristic curve, the amplitude of the voltage e is nearly constant between points a and b or points c and d irrespective of the direction of the current I but there is a hysteresis phenomenon between the points 17 and c. The phenomenon is due to the effect of the prior oscillation.

As described above, if the setting signal i is applied just before every exciting signal to the winding N of the circuit of FIG. 8, said drift of the zero point is eliminated completely, that is, a difference AI between said signal I and I becomes zero in FIG. 9, and we can obtain such an experimental relation between the input signal and the second higher harmonic voltage as shown in FIG. 10.

On the other hand, if setting signal I and the exciting signal i as shown in FIG. 4 are applied to the circuit shown in FIG. 8, we can easily realize a highly sensitive and highly accurate sign detecting circuit.

As described above, when in the circuit of FIG. 8, an exciting current i and an input signal current I are supplied, respectively, to the windings N and N a second high harmonic oscillation the phase of which is controlled by the polarity of the small signal input current I is produced in the output winding N whereby a second high harmonic voltage of large amplitude is obtained and the oscillation phase of the voltage can be surely controlled by the polarity of the small signal input current 1 The phase of the second high harmonic voltage correlates mainly to the distortion of the symmetry of the nonlinear characteristic of each element and has no relation to the unbalance between two nonlinear elements. Accordingly, variation of the characteristic of each individual nonlinear element has no direct relation to the establishment of the oscillation phase of the second high harmonic voltage, because generated harmonic current components caused by odd high harmonic voltages are very small due to the reason that the output circuit is designed so as to be resonant with only the second high harmonic component.

By the same reason as above, when the resonant frequency of the output circuit is chosen so as to tune with the frequency (f-H or f,,) in FIG. 8, and the other exciting signal of a high frequency is also applied to the winding N at the exciting period, the phase of the output voltage of the frequency (f-l-f or (f;f is subjected to the polarity of the input signal, and a sign detection of the input signal with high sensitivity and high accuracy is easily obtained.

In the circuit for obtaining a modulation product of two frequencies, the problem that the exciting signal contains even higher harmonic components is no trouble in the sign detection process, so that the exciting signal has no need of so low a value of the distortion factor with reference to waveform.

The following description is in connection with the case in which any level detection is carried out by utilizing the above-mentioned principle. In this case, one more standard reference signal winding N having the same polarity as the input winding N is added. This example is shown in FIG. 11, in which windings N N and N of a plurality of unit circuits as shown in FIG. 8 are connected respectively in series and each unit circuit is coupled to a respective parametron P P P,,. The oscillation frequencies of the second high harmonic of the exciting current i is selected so as to be equal to the oscillation frequency of the respective parametron. In the circuit of FIG, 11, when a standard direct current I is supplied to the circuit consisting of standard windings 1N 2N nN of the unit circuits, and a signal input current I is supplied to the input winding N consisting of the coils having the same number of turns, phases of the oscillation frequency in the windings 1N 2N nN coupled with the parametrons P P Pn become successively from phase to phase in accordance with the magnitude of the signal current flowing through the input winding N with successive increase of the signal input current I because the number of turns of the windings 1N 2N nN increases successively in their numerical order. Accordingly, if the oscillation phases and of the parametrons are made to correspond to the binary digit 1 and 0 respectively, the level of the signal can be directly converted to a binary digit.

In the example of FIG. 7 when the standard reference direct current I is impressed in common on all the unit circuits and effective ampere turns of the windings 1N 2N nN are set so as to be able to vary optionally, for example, by parallel connecting resistors one by one on the windings 1N 2N nN the input current I can be converted to a sign signal in any optional relationship. Moreover, in the example of FIG. 11, large and small magnitudes of the currents 1 and I are made to correspond, respectively, to the 0 phase or the 1r phase of the oscillation frequency and led out of the parametrons. However, magnitudes of the currents I and I can be led out as the positive or negative polarity of a direct current or voltage by synchronous detection of the oscillation phase of the output voltage having frequency 2 The above-mentioned principle can be applied to a detecting circuit utilizing ferroelectric elements. In FIG. 12 is shown a basic circuit for obtaining a frequency doubler by utilizing a parametric oscillation of a circuit including two ferroelectric elements. The circuit of FIG. 12 consists of two ferroelectric elements C and C two condensers C for choking the standard reference direct current voltage E and the signal direct current voltage E one coupling resistor R for impressing the voltage E on the elements C and C the other coupling resistor R for impressing the voltage E on the elements C and C and a coupling transformer T. When a high frequency control voltage e; having frequency f is impressed on terminals 3 and 4, an output voltage e having frequency 2 can be obtained from the secondary winding of the transformer T. In this example, the sequence of the voltage e; is the same as that shown in FIG. 4(A) except that current is replaced by a voltage. According to the circuit of FIG. 12, as will be well understood from the description concerning the circuits of FIGS. 3, 7 and 8, the phase of the output oscillation voltage e can be controlled in accordance with the polarity of the resultant voltage of the voltages E and E The above-mentioned examples relate to the cases in which a setting operation is indispensable for detecting the sign of the applied input signal without relation to the preceding state. However, when the circuit is so constructed that the magnetic field induced due to the input current I is perpendicular to the magnetic field due to the setting current, and a small signal input current l to be detected and an exciting current of large amplitude are supplied after demagnetization of the magnetic field induced due to the preceding input current 1 the phase of the second higher harmonic output voltage can be controlled by the instant current I An example of such a circuit as described just above is shown in FIG. 6.

The above-mentioned example relates to the case utilizing ferro-magnetic cores, but the same object can be attained by using ferro-electric elements instead of ferro-magnetic elements and by impressing a direct electric field and an alternating electric field on the elements.

In FIG. 13, a frequency doubling oscillation circuit consisting of ferroelectric elements C and CV2 each having two pairs of control terminals which are per- 9 pendicular to each other, condensers C and C for choking direct current, and a coupling transformer T.

Controlling of the circuit of FIG. 13 can be effectively attained, in the same manner as that of the circuit of FIG. 6.

The above-mentioned level detecting system relates to the case of oscillation, but the same principle may be applied to an amplification or modulation circuit.

In the above description, only one winding is used for applying the exciting signal and the setting signal to non-linear elements.

All of the above examples relate to cases in which the electric signals to be detected have been sampled. However, the present invention can be applied, with the same effect, to the case in which a continuous electric signal is used.

Now, considering the case in which a continuous input signal current is supplied as a signal current, in each magnetic core, the alternating current for demagnetizing the residual magnetism to set the core becomes an alternating bias current, thus producing a residual magnetism or a magnetic polarization made to correspond to the electric signal to be detected, .whereby an alternating output signal, the polarity of which is converted to phase or 1r phase, will be obtained.

In the other cases, the same result will be obtained. That is, even if a large magnetic field is impressed on non-linear element or elements so as to be perpendicular to fields caused by the input signal winding and the output winding, the residual polarization produced by such fields is substantially directed to a direction perpendicular to the field direction of the input winding. Accordingly, in this state, if an input signal and an exciting signal are impressed on such non-linear element or elements, a mean value of magnetic flux is established in a plus or minus state in accordance with the polarity of the input signal without relation to the preceding hysteresis phenomenon.

Then, when an alternating exciting current I of frequency f is supplied after cancelling the resultant residual magnetism or polarization directed to the input signal Winding and output winding as described above, an alternating-current output of frequency 2 the phase of which becomes 0 phase and 1|- phase in accordance with the polarity of the electric signal to be detected will be obtained.

As described in detail above, in the detecting circuit of the present invention, only the symmetrical character of the elements is utilized, and the other conditions have no direct relation to the signal discrimination. Moreover, such symmetry of the characteristics of the nonlinear elements such as a ferro-magnetic or 'ferro-dielectric body is not distorted by the outside physical conditions. Instability due to variation of the character of the non-linear element is reduced in comparison with conventional detecting devices, whereby a stable and precise sign detection of a signal can be made possible.

What we claim and desire to secure by Letters Patent 1. An electric sign detecting system comprising, an even number of non-linear elements, each having hysteresis characteristics substantially symmetrical with respect to their original point, input means for applying an input signal to said non-linear elements, setting means for applying to said non-linear elements, prior to the application of the input signal a setting signal to remove the effect of residual polarizations produced in the nonlinear elements by preceding signals applied thereto and a reference standard signal simultaneously with the application of said input signal, means connected for applying to said non-linear elements an alternating-current exciting signal, output means comprising circuit means connected to said non-linear elements in a loop configuration and including said non-linear elements for developing a signal having a frequency equal to the second high harmonic component of the exciting signal and taking out from said non-linear elements an output signal having a frequency equal to said second high harmonic component of the exciting signal and having one of two opposite phases in accordance with an algebraic sign of an algebraic difference between said input signal and said reference standard signal, and said output means having tuned means for resonating with said second high harmonic component.

2. Anelectric sign detecting system comprising two series ferroelectric elements having hysteresis characteristics substantially symmetrical with respect to their original point, means connecting said elements across said system, a transformer having a primary and a secondary winding, in parallel with said elements and capacitors in a series with said primary winding, and said primary winding having a neutral point, means connected in said system comprising terminals and resistances in series with at least one of said capacitors for applying an input signal and a reference standard signal to said series connection, and exciting terminals comprising said neutral point and a connection point intermediate said series elements for receiving in operation a setting signal for removing the eifect of residual polarization and an alternating exciting signal thereby to derive an output signal from said secondary winding of said transformer having a frequency equal to the second high harmonic component of the exciting signal and one of two opposite phases in accordance with an algebraic sign of an algebraic difference between said input signal and said reference standard signal.

3. An electric sign detecting system as claimed in claim 2, in which the two ferroelectric elements comprise means receptive in operation of an electric field perpendicular to an electric field caused by the input signal in said two dielectric elements whereby a reduced power consumption of said exciting signal is obtained.

4. An electric sign detecting system comprising two series ferroelectric elements having hysteresis characteristics substantially symmetrical with respect to their original point, circuit means connecting said elements across said system, a transformer having a primary and a secondary winding in parallel with said elements and capacitors in a series with said primary winding, said circuit means comprising said elements, said capacitors and said primary winding connected in a loop, and said primary winding having a neutral point, means connected in said system comprising terminals and resistances in series with at least one of said capacitors for applying an input signal and a reference standard signal to said series connection, and exciting terminals comprising said neutral point and a connection point intermediate said series elements for receiving in operation a setting signal for removing the effect of residual polarization and an alternating-exciting signal, thereby to derive an output signal from said secondary winding of said transformer having a frequency equal to the second high harmonic component of the exciting signal and one of two opposite phases in accordance with an algebraic sign of an algebraic difference between said input signal and said reference standard signal.

References Cited UNITED STATES PATENTS 2,927,260 3/1960 Prywes 307-88 2,968,028 1/1961 Goto et a1. 340-174 2,990,521 6/1961 Tominaga 340-174 3,184,601 5/1965 Kosonocky et al. 307-88 BERNARD KONICK, Primary Examiner.

B. HALEY, Assistant Examiner. 

4. AN ELECTRIC SIGN DETECTING SYSTEM COMPRISING TWO SERIES FERROELECTRIC ELEMENTS HAVING HYSTERESIS CHARACTERISTICS SUBSTANTIALLY SYMMETRICAL WITH RESPECT TO THEIR ORIGINAL POINT, CIRCUIT MEANS CONNECTING SAID ELEMENTS ACROSS SAID SYSTEM, A TRANSFORMER HAVING A PRIMARY AND A SECONDARY WINDING IN PARALLEL WITH SAID ELEMENTS AND CAPACITORS IN A SERIES WITH SAID PRIMARY WINDING, SAID CIRCUIT MEANS COMPRISING SAID ELEMENTS, SAID CAPACITORS AND SAID PRIMARY WINDING CONNECTED IN A LOOP, AND SAID PRIMARY WINDING HAVING A NEUTRAL POINT, MEANS CONNECTED IN SAID SYSTEM COMPRISING TERMINALS AND RESISTANCES IN SERIES WITH AT LEAST ONE OF SAID CAPACITORS FOR APPLYING AN INPUT SIGNAL AND A REFERENCE STANDARD SIGNAL TO SAID SERIES CONNECTION, AND EXCITING TERMINALS COMPRISING SAID NEUTRAL POINT AND A CONNECTION POINT INTERMEDIATE SAID SERIES ELEMENTS FOR RECEIVING IN OPERATION A SETTING SIGNAL FOR REMOVING THE EFFECT OF RESIDUAL POLARIZATION AND AN ALTERNATING-EXCITING SIGNAL, THEREBY TO DERIVE AN OUTPUT SIGNAL FROM SAID SECONDARY WINDING OF SAID TRANSFORMER HAVING A FREQUENCY EQUAL TO THE SECOND HIGH HARMONIC COMPONENT OF THE EXCITING SIGNAL AND ONE OF TWO OPPOSITE PHASES IN ACCORDANCE WITH AN ALGEBRAIC SIGN OF AN ALGEBRAIC DIFFERENCE BETWEEN SAID INPUT SIGNAL AND SAID REFERENCE STANDARD SIGNAL. 